1. Field of the Invention
The present invention relates to techniques for connecting a call originated in a line switching system to a network such as the ATM network or the like which switches packets or cells.
2. Description of the Related Art
Conventionally, it is known in general that a line in a line switching system is connected to an ATM network using a network as illustrated in a network configuration diagram of FIG. 11 in the following manner.
Referring specifically to FIG. 11, the network comprises line switch boards 100a, 100b, 100c; lines 200a, 200b, 200c in line switching systems; line conversion apparatuses 3000a, 3000b, 3000c; and an ATM network 400, wherein the line conversion apparatuses 3000a, 3000b, 3000c function as cell assembly and disassembly apparatuses. In the following, the line conversion apparatus 3000a is taken as an example to describe operations associated with the connection of a line in a line switching system to the ATM network.
The line conversion apparatus 3000a accommodates terminals in the line switching system such as the line switch board 100a and so on. On the line 200a in the line switching system, a plurality of logical communication paths (lines in the line switching system) are set (for example, three communication paths A, B, C) such that each of the communication paths A, B, C is previously corresponded permanently to another line switch board (100b or 100c) as a line switch board to be communicated. The line switch board 100a connects a call from a terminal accommodated therein to a communication path (A, B or C) corresponded to a line switch board (100b or 100c), which is the destination of the call, as a line switch board to be communicated. Conversely, the line switch board 100a connects a call from a line switch board as a communication party (100b or 100c) corresponded to each communication path, on which the call is incoming, to a destination terminal of the call accommodated in the line switch board 100a itself.
The line conversion apparatus 3000a sets a transmission virtual path to each of the communication lines A, B, C. Then, the line conversion apparatus 3000a assembles signals on the respective communication paths A, B, C incoming from the line switch board 100a into cells, adds a value indicative of a transmission virtual path, set to the communication path through which the signal has come in, to each corresponding cell as a header, and outputs the cells each having the header added thereto to the ATM network 400. The transmission virtual path is set to each communication path in such a manner that a virtual path defining a route to another line conversion apparatus (3000b or 3000c) connected to a line switch board as a communication party (100b or 100c) corresponded to the communication path is set as a transmission virtual path. The ATM network 400 transmits each cell to another line conversion apparatus (3000b or 3000c) specified in the header of the cell. Also, the line conversion apparatus 3000a sets a reception virtual path in the reverse direction to each of the communication lines A, B, C. Then, the contents of a cell incoming from the ATM network 400 are outputted to a communication path to which a virtual path indicated by the header in the cell is corresponded as a reception virtual path. In this event, set as the reception virtual path is one of virtual paths which is used as a transmission virtual path to the line conversion apparatus 3000a itself by another line conversion apparatus connected to a line switch board as a communication party corresponded to the communication path.
In the configuration described above, the line conversion apparatus 3000a always connects the communication paths A, B, C on the line 200 in the line switching system to virtual paths on the ATM network 400 to enable calls on respective communication paths on lines in the line switching system to be switched using the ATM network 400. The line conversion apparatus 3000a of the type mentioned above is described, for example, in JP-A-6-85836.